The present invention relates to the refining of hydrocarbon feedstocks. More particularly, this invention concerns the segregation and removal of coke precursors and metals from atmospheric and vacuum residua, and deasphaltened atmospheric and vacuum residua.
Hydrocarbon feedstocks, whether derived from natural petroleum or synthetic sources, are composed of hydrocarbons and heteroatom containing hydrocarbons which differ in boiling point, molecular weight and chemical structure. High boiling, high molecular weight heteroatom-containing hydrocarbons (e.g. asphaltenes) are known to contain a greater proportion of metals and carbon forming constituents (i.e. coke precursors) than lower boiling naphtha and distillate fractions. Because coke precursors form coke during thermal processing (such as is employed in a modem refinery), it is desirable to remove (or at least segregate) the heteroatom containing hydrocarbons containing the metals and coke precursors, thereby facilitating further processing of the more valuable fractions of the feedstock.
Removing coke precursors and metals from a hydrocarbon feed is not new. Long (U.S. Pat. No. 4,624,776) describes a process where resid is contacted with an adsorbent, the adsorbent is contacted with solvent having certain solubility characteristics to desorb part of the feed that is depleted in coke precursors, and then the adsorbent is contacted with a second solvent with different solubility characteristics to desorb a second portion of the feed that is enriched in coke precursors. Bowes (U.S. Pat. No. 4,486,298) describes a demetallation process where an aromatic solvent, such as benzene, or cyclic, non-aromatic solvent, such as cyclohexane, is required to be added to the feed in order to disperse the metal containing compounds. The mixture is then contacted with an adsorbent to remove a major portion of the metal containing compounds. In the present invention, a feed, either resid or the deasphalted oil from a solvent deasphalting unit, containing coke precursors and metal containing compounds is contacted with an adsorbent without the need for additional solvent